The invention relates to a method for producing a holding configuration for at least one sheathed optical fiber conductor.
Such holding configurations are used, for example, for connecting an optical fiber conductor end to an electrooptical module, or for coupling to corresponding plug connectors. Holding configurations, as an end piece which can be coupled, can directly terminate the optical fiber conductor, which is sheathed by a protective sheath, or can surround a section of the optical fiber conductor located in front of the end, so that the optical fiber conductor runs on both sides of the holding configuration. In each case, the holding configuration has at least one end (which is called an outlet opening in the following text) of a through-channel for holding the optical fiber conductor, from which end the optical fiber conductor emerges.
U.S. Pat. No. 4,984,865 discloses a holding configuration for an optical fiber conductor which emerges from a cable sheath end together with ends of a strain relief device in the form of strands (aramide fibers). The cable sheath end is inserted into a plug connector housing, which is filled with a thermoplastic. It is not possible for unacceptably small bending radii of the optical fiber conductor to occur in the case of that known holding configuration, since the optical fiber conductor is completely surrounded by the thermoplastic and runs in a fixed manner within the holding part.
German Patent DE 27 11 670 C2 discloses a holding configuration in the form of a detachable plug connector, in which two optical fibers to be coupled are each bonded by their end region into a centering insert. The latter is inserted into one end of a tube, which is used as a guide body and can be inserted with the corresponding coupling partner into an adjustment capillary, in order to make contact at the end.
In the case of the holding configuration of the type mentioned initially, which is known from German Published, Non-Prosecuted Patent Application DE 43 03 737 A1, corresponding to U.S. Pat. No. 5,574,819, a cable end, which has been freed at the end of its cable sheath revealing strain relief device ends and two optical fiber conductor ends which are sheathed by one protective sheath (buffer) in each case, enters an inlet opening of a receptacle. A spreading sleeve is inserted into the cable sheath end and expands the sheath beyond the inlet opening width. The optical fiber conductors pass through a through-channel which runs from the inlet opening to an outlet opening, and leave the receptacle with radial freedom of movement. The receptacle is partially filled with a fixing compound. That surface of the cured fixing compound which is close to the outlet opening (filling level) is located vertically at a distance below the outlet opening in the longitudinal axis direction when the configuration is oriented vertically.
If the cable end, once it has been provided with the holding configuration, is handled incorrectly or carelessly in the rest of the production or assembly process, there is a risk of the optical fiber conductors being bent over the comparatively sharp-edged contact line to the surface of the fixing compound.
That problem is exacerbated if fixing compounds are used which raise up the optical fiber conductors due to adhesion effects and capillary forces. Specifically, in practice, it has been found with through-channels having a cross section which is dimensioned to be only slightly greater than the cross section of the sheathed optical fiber conductor, that the fixing compound, when in the flowing state, rises to an undesirably high extent above the desired filling level due to capillary effects, and consequently forms sharp edges which lie against the optical fiber conductor, closely underneath the outlet opening. On one hand, if optical fiber conductors are bent beyond their critical bending radii, they can be irreversibly damaged. Such damage may temporarily remain concealed by the protective sheath in a disadvantageous manner, and not be detected until final inspection or initial operation. On the other hand, comparatively narrow through-channels are desirable in order to achieve adequate adhesion forces, the necessary amount of fixing compound and its curing time.
In order to overcome that problem, production and assembly have until now had to be carried out extraordinarily carefully, with the optical fiber conductors temporarily being fixed in appropriately constructed production holders at least until additional, permanent structural elements (for example separate kink protection elements) or appropriate housings with guides were fitted.
It is accordingly an object of the invention to provide a method for producing a holding configuration for at least one sheathed optical fiber conductor, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and which, even immediately after fitting and curing of a fixing compound, and without any additional apparatuses, ensure reliable protection of the sheathed optical fiber conductor against unacceptably small bending radii.
With the foregoing and other objects in view there is provided, in accordance with the invention, a holding configuration, comprising a fixing compound; a receptacle for receiving the fixing compound, the receptacle having an inlet opening for receiving an end of an optical fiber cable stripped at the end to expose an optical fiber conductor, and the receptacle having an outlet opening through which the optical fiber conductor emerges with radial freedom of movement and free of the fixing compound fixing a section of the optical fiber conductor; and a spreading body at least partially inserted into an end of a cable sheath of the optical fiber cable, the spreading body bounding a through-channel expanded from a first cable section closely surrounding the optical fiber conductor to a second cable section opening into the outlet opening, the second cable section having a cross section dimensioned relative to a cross section of the optical fiber conductor for maintaining the fixing compound in the second cable section substantially free of capillary forces.
While capillary force effects on the fixing compound are achieved in the first, narrower section, in order to fix the optical fiber conductor safely while using little material, as long as the fixing compound is still a low-viscosity liquid, the deliberate expansion of the through-channel results in the capillary effects in the second section being suppressed in a defined manner. On one hand, the amount of fixing compound to be introduced can thus be considerably reduced in an advantageous manner since it is necessary to fill only a comparatively narrow gap between the optical fiber conductor and the wall of the first section. Since, on the other hand, the expansion reliably prevents the fixing compound, which can still flow, from flowing on or rising undesirably in the direction of the outlet opening, the amount of fixing compound can be dimensioned and introduced without so much care being required in particular with regard to capillary effects. The amount of fixing compound is preferably dimensioned in such a way that the optical fiber conductor remains largely free of fixing compound in the second section. In consequence, the optical fiber conductor has radial mobility even at the start of the expanded section, and that has a positive influence on the bending geometry, which is governed by the last fixing point, close to the outlet opening, of the optical fiber conductor. The expansion allows the distance between the fixing point and the outlet opening to be set as planned, and to be easily controllable.
The maximum angles or bending radii of the optical fiber conductor which occur during the production and assembly processes (without deliberate overbending) are automatically kept comparatively gentle in conjunction with rounding of the rims or edges of the outlet opening which may come into contact with the optical fiber conductor. The maximum angle which can occur on its own, without deliberate action, between the longitudinal axis of the holding configuration and the optical fiber conductor is preferably less than 45xc2x0.
In accordance with another feature of the invention, the second channel section expands to approximately twice the width of the first channel section. This provides a particularly preferred cross-sectional ratio of the channel sections.
In accordance with a further feature of the invention, the expansion from the first channel section to the second channel section is constructed like a step, which permits a specially defined control of the capillary effects according to a preferred development of the invention.
In accordance with an added feature of the invention, the spreading body has two essentially parallel webs which extend radially outward as far as the rim of the receptacle and bound the outlet opening. The spreading mandrel, in combination with the receptacle, forms an outlet opening with its webs which is specifically constructed for the optical fiber conductor and has a size and contour that can be dimensioned in order to reliably avoid bending radii less than the minimum.
As a supplementary function, the webs according to an advantageous version of the invention can interact with at least one positioning projection on the holding part side, which produces a defined position and secures the spreading body against twisting.
In accordance with still another feature of the invention, the spreading body has a shaft.
In accordance with an additional feature of the invention, the narrow channel section is formed by an axial groove in the spreading body, so that the optical fiber conductor is guided particularly exactly along the spreading body.
In accordance with yet another feature of the invention, a ratio of the diameter of the optical fiber conductor including the sheath, to the width of the second channel section and to a distance between the expansion and the outlet opening, is approximately 1:2:5. This has been found to be particularly advantageous with regard to the physical structure. In practical tests, with the sheathed optical fiber conductor having a diameter of 1 mm, it has been found to be particularly advantageous for the distance between the expansion and the outlet opening to be at least 5 mm.
With the objects of the invention in view there is also provided a method for producing a holding configuration for at least one sheathed optical fiber conductor, which comprises forming a holding body with a through-channel having a first channel section expanded over an expansion region into a second channel section opening into an outlet opening having a rounded rim; applying a fixing compound from the outlet opening into the expansion region for fixing a section of an optical fiber conductor introduced or to be fitted into the first channel section; dimensioning a width of the first channel section for exerting capillary forces on the fixing compound contributing to filling a gap between the optical fiber conductor and the first channel section, and dimensioning a width of the second channel section for maintaining the fixing compound in the second channel section free of capillary forces; and metering the fixing compound for permitting the optical fiber conductor to emerge through the outlet opening with radial freedom of movement and free of fixing compound.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for producing a holding configuration for at least one sheathed optical fiber conductor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.